linux-kernel - Re: [PATCH v1 1/4] ASoC: codecs: tfa989x: Add switch to allow disabling amplifier

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Date:   Mon, 25 Oct 2021 11:52:04 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Vincent Knecht <vincent.knecht@...loo.org>
Cc:     stephan@...hold.net, lgirdwood@...il.com, robh+dt@...nel.org,
        perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH v1 1/4] ASoC: codecs: tfa989x: Add switch to allow
 disabling amplifier

On Sun, Oct 24, 2021 at 10:58:37AM +0200, Vincent Knecht wrote:
> From: Stephan Gerhold <stephan@...hold.net>
> 
> In some configurations it may be necessary to explicitly disable
> the amplifier with an ALSA mixer. An example for this is a stereo
> setup with two TFA989X. If only one of them should be used (e.g.
> to use it as an earpiece) the other one must be explicitly disabled.
> 
> Add a virtual "Amp Switch" to implement that. There is no register
> for this (SND_SOC_NOPM) so it only prevents DAPM from activating
> the amplifier. Also it is inverted (= enabled by default) for
> compatibility with devices that do not need this functionality.

Why can you not use a standard pin switch on the speaker output for
this?

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